Goitrogens and Cruciferous Vegetables

There has been a huge rise in hypothyroidism in recent times, particularly in women, and much attention has been directed by scientists and physicians to the so called goitrogenic foods – cruciferous vegetables. Goitrogens are foods that inhibit bodily uptake of iodine, or that inhibit the utilisation of iodine by the thyroid gland, and so are implicated in hypothyroidism, related goitre formation, and thyroid cancer. Goitrogens also inhibit the transfer of iodine to breast milk. At the same time, these foods are widely touted by scientists and physicians to have anti-cancer and detoxifying properties, and strangely enough, both the pro and con arguments for cruciferous vegetables revolve around the same group of compounds – the glucosinolates.

The different forms of glucosinolates in crucifers are broken down in the body to three groups of compounds: isothiocyanates, indoles, and nitriles. All three groups have been studied for either potent anti-carcinogenic, detoxification, anti-viral, or anti-bacterial properties. All three groups have also been identified as potentially harmful, with effects such as inhibition of thyroid hormone production, and tissue-based cyanide toxicity having been experimentally demonstrated. A word of caution here: many experiments are conducted at higher doses than would be found in food, on isolated compounds only (so not as found in nature), and obviously, rarely on humans. Regardless of this caveat, we tend to base our choices on what these kinds of experiments show us, and when there is conflicting advice, we can be understandably confused.

First, we should understand that glucosinolates are a part of the crucifer defence mechanism against herbivory. They are inert substances until activated by the accompanying enzyme myrosinase. In the plant tissue, glucosinolates and myrosinase are segregated, but the action of chewing breaks down the compartment walls, and the formation of what is fundamentally a range of irritant and toxic chemicals is initiated. In humans, high doses of these toxins are required to initiate substantial effects. For example, isothiocyanates are metabolised in the body into two functional groups: thiocyanate ions and thioureas, with the former being produced in much larger numbers. Thiocyanate ions inhibit uptake of iodine by the thyroid gland, but this can be ameliorated by a sufficiency of iodine in the diet. Thioureas, however, shut down the enzyme that allows iodine to be used in the manufacture of thyroid hormones. In a nut shell, dietary iodine can allow the body to cope with low levels of isothiocyantes, but not high levels. The effects of iodine deficiency are exacerbated by a bodily lack of vitamins A and E, zinc and iron. This indicates that while crucifers confer health benefits. we should eat them sparingly, and ensure we have adequate dietary iodine, selenium, zinc, iron, and vitamins A and E. In other words, we could say treat crucifers as a medicine food that fits into a well balanced diet, one in which they are not eaten in great quantity.

Reduction in thyroid function may result from many factors, and these often occur in concert, and on a regular basis. A few quick examples of this are: habitual use of refined sugars and starches, particular without fats or protein as balance, depletes the thyroid of hormones as these are part of the emergency blood sugar balancing response of the body; repeated exposure to endocrine disrupters that inhibit thyroid activity such as fluoride (in drinking water), and phytoestrogens, (for example from soy products); exposure to dioxins, PCBs, EBDCs and perchlorate; and exposure to high levels of ionising radiation (including X-rays). Even though endocrine disrupters work in concert, they are studied in isolation, so the combined effects of disrupters on thyroid function are most likely greatly in excess of any single effect reported in scientific literature. Disruption of thyroid function may be tied to overall hormonal imbalance, and it is worth noting that women are more likely to become hypothyroid immediately after childbirth, and after menopause. Avoidance of known external endocrine disrupters is therefore of particular importance to women, and hormonal means of birth control must be included in this consideration.

The fermentation of food does not destroy goitrogens, cruciferous vegetables need to be well boiled for an extended period to reduce the goitrogen content by 90%. But then, fermented foods are only ever intended to be a condiment, and one addition to a well balanced diet. The inclusion of cruciferous vegetables to ferments conveys many health benefits, and there is no reason not to ferment them as long as we maintain adequate dietary inputs of iodine, selenium, zinc, iron, and vitamins A and E. Here is a list of good thyroid foods, but remember, they must be organic to be most beneficial: most seafoods (though amounts vary depending on iodine in home waters), kelp and other seaweeds (reliable high levels, the best source), unrefined sea salt, Himalayan salt, fish and bone broths, dark green vegetables (though some report that spinach blocks iodine absorption), butter and other dairy (preferably raw), eggs, kefir and yogurt, oregano, strawberries, cranberries, artichokes, asparagus, and navy beans.

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